/*
 * Copyright (c) 2018-2020 "Graph Foundation,"
 * Graph Foundation, Inc. [https://graphfoundation.org]
 *
 * This file is part of ONgDB.
 *
 * ONgDB is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
/*
 * Copyright (c) 2002-2020 "Neo4j,"
 * Neo4j Sweden AB [http://neo4j.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.neo4j.cypher.internal.runtime.interpreted.pipes

import org.neo4j.cypher.internal.runtime.interpreted.ExecutionContext
import org.neo4j.cypher.internal.runtime.interpreted.commands.expressions.{Expression, NumericHelper}
import org.neo4j.cypher.internal.util.v3_4.attribution.Id

import scala.collection.AbstractIterator
import scala.collection.Iterator.empty

case class LimitPipe(source: Pipe, exp: Expression)
                    (val id: Id = Id.INVALID_ID)
  extends PipeWithSource(source) with NumericHelper {

  exp.registerOwningPipe(this)

  protected def internalCreateResults(input: Iterator[ExecutionContext], state: QueryState): Iterator[ExecutionContext] = {

    if (input.isEmpty) return empty

    val limit = asPrimitiveLong(exp(state.createOrGetInitialContext(executionContextFactory), state))

    new AbstractIterator[ExecutionContext] {
      private var remaining = limit

      def hasNext: Boolean = remaining > 0 && input.hasNext

      def next(): ExecutionContext =
        if (remaining > 0L) {
          remaining -= 1L
          input.next()
        }
        else empty.next()
    }
  }
}
